Presently available air and fluid brake cylinders typically comprise a single piece, cast iron U-shaped cylindrical housing, in which a spring loaded piston head and piston shaft reciprocate to actuate a brake mechanism operatively connected to the piston shaft. The piston head includes a circumferential seal and wear ring that provides the primary load bearing contact between the cylinder bore and the piston, as well as preventing by-pass leakage. The piston shaft extends outward through an opening in the metal housing. The introduction of pressurized fluid, such as air into the cylinder and against the piston head forces the piston shaft to move with respect to the cylinder, and to activate the brake mechanism through movement of the piston shaft. A spring, or other counterbalancing force mechanism, is compressed as the piston head moves under the influence of the pressurized air into the cylinder, and the spring returns the piston head and piston shaft to its non-activated position when air pressure is relieved from the piston head. FIG. 1 is a cross-sectional view of a typical air brake cylinder assembly of the prior art.
The piston head seal and wear ring, as it reciprocates in the cylinder, comes into frictional contact with the cast iron inner wall of the cylinder, causing the piston head to wear upon each movement. This wear results in air leakage around the piston head and a reduction in the air pressure force available to move the piston shaft against the force of the spring to activate the attendant brake device.
The present invention provides a brake cylinder assembly that overcomes these problems by incorporating a relatively low-friction composite material to form a cylinder tube, and an assembly of light weight, corrosion resistant materials to encase the composite cylinder tube under compression, wherein internal pressure resulting from operation of the piston assembly provides a hoop stress in the composite cylinder tube.
The present invention also provides a brake cylinder assembly having a composite cylinder tube that has a relatively low coefficient of friction, an excellent surface finish, and the ability to allow lubricant to migrate to the wear surface between the cylinder wall and the piston head, thus extending seal and wear ring life.
The present invention also provides a combination of a composite cylinder tube and a metallic framework structure applying a compression force to the cylinder tube, resulting in the application of an axial stress in the composite cylinder tube and corresponding reaction forces in the metallic framework structure.
The present invention also provides a composite tube and metallic structure combination that applies a constant compressive stress to the composite tube, resulting in tensile stresses in lateral beams of the metallic structure.
The present invention also provides a compression force near, but not exceeding, the compression strength of the composite cylinder, which takes advantage of the elastic properties of continuous glass fiber reinforced composite structures with specific fiber orientations.